FR2800126A1 - CONTROLLED SELF-IGNITION COMBUSTION PROCESS AND FOUR-STROKE ENGINE ASSOCIATED WITH TRANSFER DUCTS BETWEEN EXHAUST DUCT AND INTAKE DUCT - Google Patents

Abstract

The control procedure, for use on a multi-cylinder 4-stroke engine with each cylinder (1) having at least one inlet (2) and exhaust (3) duct, consists of taking a quantity of the exhaust gas from one cylinder when the engine is under partial load and transferring it to the inlet duct of another via valves (4, 7). During the transfer the gas can be thermally insulated and/or reheated by catalysis in a common transfer duct (5). At the same time as the gas is heated, the catalyst (10) can be used to reduce the pollutants in it.

Description

1i 2800126 The present invention relates to internal combustion engines

  4-stroke with controlled self-ignition. Controlled self-ignition is a known phenomenon in 2-stroke engines. This type of combustion has advantages in terms of pollutant emissions: in particular, low emissions of hydrocarbons and nitrogen oxides are obtained. In addition, a remarkable

  cyclical regularity is achieved during self-ignition combustion.

  Self-ignition is a phenomenon which allows combustion to be started thanks to residual burnt gases which remain in the chamber

after combustion.

  Self-ignition is carried out by controlling the quantity of residual gases and its mixture with the fresh gases (not yet burnt). Residual gases (hot burnt gases) initiate the combustion of fresh gases through

  a combination of temperature and presence of active species.

  In 2-stroke engines, the presence of residual gases is "inherent" in combustion. In fact, when the engine load decreases, the quantity of fresh gas decreases, which leads to an increase in the quantity of residual gas (burnt gas from the previous cycle or cycles which have not left the cylinder). The 2-stroke engine therefore works with an internal circulation (or internal EGR) of the burnt gases at partial load. However, the presence of this internal EGR is not

  not sufficient to obtain the desired function in self-ignition.

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  Researchers' work also shows that it is necessary to control and limit

  the mixture between this internal EGR and the fresh gases.

  The controlled self-ignition technology applied to the four-stroke engine is particularly interesting because it makes it possible to operate this type of engine with an extremely diluted mixture, with very low richness and consequently, oxide emissions.

ultra low nitrogen.

  However, this technology comes up against an important technological difficulty which is the fact that to obtain it without benefiting from the internal EGR effect of the 2-stroke engine, it is necessary either to greatly increase the compression ratio of the engine (with knocking problems at high load), either to heat very strongly (several hundred degrees Celsius) the fresh gases admitted, or

combine the two phenomena.

  Solutions exist to reduce the pressure and temperature requirements for 4-stroke engines, in particular by the use of appropriate additives added to the fuel. The request of

  French patent FR 2 738 594 illustrates a solution of this type.

  For 4-stroke engines, it is known, in particular by international application WO-93/16276, to combine a variable timing of the distribution with a non-return system at the intake in order to reduce the losses by pumping under load partial. This solution allows

  then operate with the intake valve as open as possible.

  Patent application FR-97 / 02.822 filed in the name of the applicant describes a self-ignition control in a four-stroke engine. More specifically, this document recommends, at partial load, to minimize the mixing of fresh gases with the burnt gases enclosed in the combustion chamber, by acting on the closing of the exhaust. It is therefore a solution close to the technique of

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  "internal" recycling which allows stratification of the gases in the combustion chamber. Patent application FR-97 / 11,279 filed in the name of the applicant also aims to minimize, at partial load, the mixing of fresh gases with the burnt gases contained in the combustion chamber,

  in order to control and promote self-ignition combustion.

  However, this teaching proposes to transfer the burnt gases from

  the exhaust of a cylinder into the intake of the same cylinder.

  This solution creates a very significant dilution of the burnt gases recycled, by the air, before entering the combustion chamber, which can be problematic. The present invention aims to achieve controlled self-ignition in multi-cylinder 4-stroke engines which is very simple, therefore reliable, easy to implement and which maximizes the stratification of the gases burned in the combustion chamber. In addition, the burnt gases retain or even increase, according to the invention, their

  temperature which is favorable for self-combustion.

  Thus, the subject of the present invention is a method of combustion by controlled self-ignition of a 4-stroke engine comprising several cylinders each having at least one intake orifice and at least one exhaust orifice, the orifices and the control means of the closure being conventional, that is to say according to the knowledge of a person skilled in the art. The invention can be applied to injection engines

direct (FDI) or indirect.

  According to the invention, the method consists during partial load operation, to transfer via an appropriate transfer means of the exhaust gases from a cylinder, generally in the exhaust phase, to another cylinder, generally in the intake phase . The exhaust gases are led, via a specific valve placed after the exhaust means, to the means of

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  transfer. Thanks to a second valve, the exhaust gases transferred

  arrive in the intake duct, upstream of the intake means.

  For more efficiency, it is desirable that an intake means is dedicated to the entry of exhaust gases into the cylinder (in this case at least two intake means are required) to reduce the mixture between

fresh and burnt gases.

  Exhaust gases can also be recovered from a cylinder at the end of the expansion phase. They can also be introduced into a

  another cylinder at the start of the compression phase.

  The method according to the invention also consists in controlling the distribution of the flow rate of the exhaust gases between the exhaust system and the transfer means. In addition, the method may consist in thermally insulating and / or heating the exhaust gases transferred into said appropriate transfer means, in order to

  further improve self-ignition.

  In order to heat the burnt gases passing through the transfer means, catalysis means can be placed in the transfer means. The positioning of the catalyst is a compromise between positioning close to the cylinder intake valve, in order to have a higher temperature of the burnt gases when they enter the cylinder, or then close to the exhaust valve, in order to facilitate the priming of this catalyst during cold starts. In addition to the fact that this catalyst has the primary function of heating the burnt gases to facilitate controlled self-ignition, in the case of cold start, it will participate, from its initiation, in the reduction of polluting emissions during a phase o the catalyst the main pot is usually not fully primed. The catalysis means can comprise a mass of catalyst or walls coated with catalyst. In this place, at full load, the catalyst does not receive the burnt gases, therefore does not risk

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  no early deterioration and does not create a loss of additional loads. Indeed, at full load, the transfer means no longer communicate with the conduits associated with the exhaust and intake orifices of the cylinders. At full load, the engine configuration becomes conventional. In order to increase the temperature of the exhaust gases at partial load, the richness of the exhaust gases can be increased, in particular in the case of a direct injection engine. In this case, a fuel injection at the end of the exhaust phase allows the exhaust gases to increase in temperature thanks to the reaction in the catalyst. It is possible to place a fuel injector

  specific upstream of the catalysis means.

  According to one embodiment of the invention, a conduit is used

  common for the transfer of exhaust gases.

  According to another embodiment of the invention, there is used for the transfer of the exhaust gases, a set of conduits connecting the specific exhaust conduits to the specific intake conduits

two by two.

  The present invention further relates to a 4-stroke internal combustion engine operating in controlled self-ignition and comprising several cylinders each having at least one inlet orifice and at

minus an exhaust port.

  According to the invention, each cylinder further comprises a specific means intended for the passage of exhaust gases from the exhaust of a cylinder, generally in the exhaust phase, to at least one other cylinder, generally in the phase of admission, as well as an associated means of transfer, the transfer taking place during the

partial load operation.

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  A means of thermal insulation and / or heating of the means of

  transfer can also be provided without departing from the scope of the invention.

  Advantageously, the engine further comprises means for distributing the exhaust gases between the exhaust system and the transfer means, at partial load. In addition to the specific valve for diverting (totally or partially) the exhaust gases towards the transfer means, the exhaust gas distribution means may comprise means

  valve placed near the exhaust means.

  According to one embodiment, said transfer means comprises

a common conduit.

  In accordance with another embodiment of the invention, the transfer means comprises a set of conduits connecting the specific exhaust conduits and valves to the conduits and valves

  specific admission two by two.

  Other features, details, advantages of this

  invention will appear more clearly on reading the description which

  will follow, made by way of illustration and in no way limitative with reference to the appended drawings in which: - Figure 1 is a schematic section of an embodiment of the invention; - Figure 2 is a schematic section of another embodiment

of the invention.

  - Figure 3 shows a variant for the two previous modes.

  FIG. I illustrates the case of an engine having four cylinders 1.

  The invention in fact applies to all engines comprising at least

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  two cylinders. The letter A represents the admission in a cylinder, the letter E

  the exhaust in the same cylinder.

  Each cylinder i comprises at least one orifice 2 for admitting a charge. The present invention preferably includes two intake ports (as shown in the figures). By means of admission of a load, it is necessary here to understand: an intake orifice with which is associated a valve and the duct associated with this orifice. So

  equivalent, the same is true for the name exhaust means.

  Each cylinder further includes an exhaust port 3

  conventionally equipped with an associated conduit and valve.

  In addition, each cylinder 1 comprises distribution means of the valve type 4 placed in the exhaust duct, obviously downstream of the exhaust orifice. This valve, or equivalent device, allows the burnt gases leaving the exhaust orifice to go into a transfer means 5. In this variant, the transfer means 5 is a conduit which communicates with all the conduits

  cylinder exhaust, as well as with all intake ducts.

  It is these distribution means which make it possible to control the rate of transfer of gases between the exhausts and the inlets. In full

  load, these valves 4 close the communication to the conduit 5.

  Each cylinder i also comprises a valve 7 placed in the intake, close to the intake orifice 2. It allows the burnt gas to go from the transfer means 5 to the cylinder 1, via the distribution valve 7 and the inlet port 2. When fully loaded, these valves 7 are

preferably closed.

  In each cylinder, a valve means 6 is arranged near the exhaust means 3. An appropriate and coordinated control controls the opening of each valve means 4, 6, 7, and makes it possible to regulate and distribute the flow of gas between exhaust

  and the transfer medium 5.

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  It is possible, without departing from the scope of the invention, not to

consider winnowing 6.

  At partial load, exhaust gases are transferred from a cylinder generally in the exhaust phase to another cylinder generally in the intake phase. The table below illustrates the transfers thus carried out on a

cycle, for a 4-cylinder engine.

  CYLINDER 1 CYLINDER 2 CYLINDER 3 CYLINDER 4

THIS SIDE

E> A D C

A C E D

C D A E

  D = relaxation; E = exhaust; A = admission; C = compression The present invention can use a standard distribution for the opening of all the exhaust and intake valves. In this case, at partial loads, the burnt gases and the fresh gases will enter together

  in the cylinder in the intake phase.

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  In the case where a known system of variable valve opening is available, some strategies can be effectively used with the present invention: - For the exhaust, in the case of at least 2 exhaust means (3 and 3 ' ), the orifice 3 for the fresh gases can be slightly opened at the beginning of the exhaust and the orifice 3 ′ associated with the valve 4, normally open then forces the burnt gases to go towards the transfer means 5. This strategy allows to send a larger amount of burnt gas in the transfer means 5 and therefore in the other cylinder in the intake phase. By slightly open, it should be understood that one acts on the height of the valve lift, or on the duration of the lift, or on both. In this case, winnowing 6 is not necessary. The opening of the orifice 3 ′ can also begin and / or take place during the end of the expansion time in order to recover very hot and pressurized burnt gases. It can also be used to quickly heat the catalyst 10 when

cold start.

  - For admission, in the case of at least 2 admission means, orifice 2 can be opened at the start of the admission phase and quickly closed. The orifice 2 ′ is then opened at the end of the intake phase, limiting the crossing between the valves 2 and

  2 'in order to limit the mixing of the burnt gases with the fresh gases.

  This configuration allows, with an adequate strategy for managing the exhaust valves, to increase the pressure in the cylinder by forcing the entry of burnt gases after the entry of the charge of fresh gas. The entry of the burnt gases can also be terminated during the start of the compression time to increase the quantity of burnt gases (if the pressure available

  in the transfer medium allows).

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  Another possibility is to first bring the burnt gases into the cylinder through the orifice 2 ', and then bring the charge through the orifice 2, with a limited valve crossing in order to limit the mixing of the burnt gases. and fresh gas. It will not depart from the scope of the present invention if the fresh gases

  are compressed, for example by a compressor.

  According to an embodiment of the invention, illustrated by FIG. 1, the transfer means comprises a common conduit with accesses to

  all specific valves 4 and 7.

  It is also conceivable, without departing from the scope of the invention, to provide as a transfer means a set of conduits connecting the specific exhaust ducts and valves to the specific intake ducts and valves two by two, and which allow by example for

  a four-cylinder engine, to have the transfers according to the table below

  1 5 above as illustrated in Figure 2.

  Advantageously, the transfer tube or tubes 5 can be thermally insulated, using a ceramic 8 for example. It can also be heated by specific means 8 '. Thus the gases which pass through a transfer pipe 5 do not lose, or even gain calories when they arrive in the cylinder. Self-ignition is thus improved since it is known that the temperature of the recycled gases is an important parameter, which promotes self-ignition. A catalyst 10 can also be used in order to heat the burnt gases and advantageously, at the same time, to reduce the rate of pollutants

  present in the burnt gases passing through the transfer means 5.

  Figure 3 shows a variant where the exhaust has only one orifice. It is clear that the means of admission, like exhaust, are not limited to a double exhaust and a

double admission.

  The present invention has the definite advantage of not needing specific transfer orifices, since it uses the conventional intake and exhaust ducts of the four-stroke engine considered.

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Claims (12)

  1) Method of controlling combustion by self-ignition of a 4-stroke engine comprising several cylinders (1) each having at least one intake means (2) comprising an intake duct and at least one exhaust means (3) comprising an exhaust duct, characterized in that, during partial load operation of said engine, an amount of exhaust gas is taken from the exhaust duct of a cylinder, and an amount of burnt gases to the intake duct of at least one other cylinder. 2) Process according to claim 1, in which one isolates   thermally and / or the transferred exhaust gases are reheated.   3) Method according to claim 2, wherein the gases are heated   by catalysis in the transfer conduits.   4) Method according to any one of the preceding claims,   in which the flow rate of the transferred gas is regulated.   ) Method according to any one of the preceding claims,   in which a common conduit (5) is used for the transfer of the exhaust gases.   6) Method according to one of the preceding claims, in which,   at full and heavy loads, no exhaust gas is collected or transferred.   7) Method according to any one of claims 1 to 4, in   which is used for the transfer of exhaust gases, a set of 13 2800126   ducts connecting the specific exhaust ducts to the ducts   specific admission two by two.   8) 4-stroke internal combustion engine operating automatically   controlled ignition and comprising several cylinders (1) each having at least one intake means (2) comprising an intake duct and at least one exhaust means (3) comprising an exhaust duct, characterized in that each cylinder (1) comprises means (5) for transferring exhaust gases from said exhaust duct from a cylinder to an intake duct of at least one other cylinder.   9) Internal combustion engine according to claim 8, wherein the transfer means further comprises an isolation means   thermal (8) and / or heating (8 ') of said transferred gases.   ) Internal combustion engine according to any one of   claims 8 or 9, wherein said exhaust means (3)   includes means for controlling (4) the communication between the conduit   exhaust and the conduit (5) of the transfer means.   11) Internal combustion engine according to claim 10, wherein said intake means (2) comprises means for controlling (7) the communication between the intake duct and the duct of the means transfer (5).   12) Internal combustion engine according to any one of   claims 8 to 11, wherein said transfer means comprises a   common duct (5) which communicates with the intake ducts and   exhaust of each of the cylinders.   13) Internal combustion engine according to any one of   claims 8 to 12, wherein said transfer means   include catalysis means (10). 14 2800126   14) Internal combustion engine according to any one of claims 8 to 11, wherein said transfer means   include a set of conduits connecting the specific exhaust valves to the specific two-by-two intake valves.   15) Internal combustion engine according to one of claims 8 to   14, in which it has only one exhaust orifice.